《Bulk_micromachining_of_silicon》.pdf

Bulk Micromachining of Silicon GREGORY T. A. KOVACS, MEMBER, IEEE, NADIM I. MALUF, MEMBER, IEEE, AND KURT E. PETERSEN, FELLOW, IEEE Invited Paper Bulk silicon etching techniques, used to selectively remove The geometries of etched features lie along a continuum silicon from substrates, have been broadly applied in the between fully isotropic (rounded, due to equal etch rates fabrication of micromachined sensors, actuators, and structures. in all directions) to anisotropic (typically exhibiting per- Despite the more recent emergence of higher resolution, surface- micromachining approaches, the majority of currently shipping fectly flat surfaces and well-defined, sharp angles). This is silicon sensors are made using bulk etching. Particularly in illustrated in Fig. 1(a) and (b). These properties are defined light of newly introduced dry etching methods compatible with by the nature of the chemical reactions, the diffusion of complementary metal–oxide–semiconductors, it is unlikely that reactants and products, and a number of other factors, bulk micromachining will decrease in popularity in the near including the shapes of the masks used to define the etched future. The available etching methods fall into three categories in terms of the state of the etchant: wet, vapor, and plasma. For each regions. category, the available processes are reviewed and compared Another key distinguishing feature of etchants is the in terms of etch results, cost, complexity, process compatibility, phase of the reactants: liquid (or “wet” etchants, almost and a number of other factors. In addition, several example exclusively relying on aqueous chemistries), vapor, and